Field of the Invention
Embodiments described herein generally relate to drying of wet substrates in a post chemical mechanical polishing cleaning apparatus. More specifically, embodiments described herein relate to a substrate drier for a post chemical mechanical polishing cleaning apparatus.
Description of the Related Art
As semiconductor device geometries continue to decrease, the importance of ultra clean processing increases. Post chemical mechanical polishing (CMP) cleaning is traditionally a wet process performed to clean and completely dry a substrate without leaving any particles or residue on the substrate, which can negatively affect yield. In the process of drying the wet substrate, any particles in the solution present on the substrate prior to drying may reattach to the substrate and remain on the substrate after drying.
A method known as Marangoni drying creates a surface tension gradient to induce bath fluid to flow from a substrate in a manner that leaves the substrate virtually free of the bath fluid, and thus may avoid streaking, spotting, and residue marks on the substrate. During Marangoni drying, a solvent miscible with the bath fluid (i.e., isopropyl alcohol (IPA) vapor) is introduced to a fluid meniscus which forms as the substrate is lifted from the bath or as the bath fluid is drained past the substrate. The solvent vapor is absorbed along the surface of the fluid. The concentration of the absorbed vapor is higher at the tip of the meniscus. The higher concentration of absorbed vapor causes surface tension to be lower at the tip of the meniscus than in the bulk of the bath fluid, causing bath fluid to flow from the drying meniscus toward the bulk bath fluid. Such a flow is known as a “Marangoni” flow and can be employed to achieve substrate drying without leaving streaks, spotting, or bath residue on the substrate.
Aqueous cleaning with a tank of fluid, such as a bath having a solution described above, followed by a rinsing bath (i.e., within a separate tank, or by replacing the cleaning tank fluid) in a Marangoni process generally requires the substrate to be drawn through a bath with a large volume. As such, the entire substrate may be submerged in the tank during certain portions of the cleaning process. Particles introduced into the tank can accumulate in the tank reattach onto the substrate. The problem of particle reattachment may be reduced by creating a fluid flow within the tank. However, apparatuses used to move the substrate through the tank may prevent optimal fluid flow needed to reduce reattachment of particles to the substrate.
Thus, what is needed in the art is an apparatus to prevent reattachment of particles to a substrate in a post CMP drying process.